The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
An internal combustion engine (ICE) may use a sequential turbocharger to increase torque output by delivering additional air into cylinders of the ICE. The sequential turbocharger may be a two-stage turbocharger system. The sequential turbocharger may include a high-pressure turbocharger and a low-pressure turbocharger that are arranged in series. The high-pressure turbocharger may include a high-pressure turbine and a high-pressure compressor. The low-pressure turbocharger may include a low-pressure turbine and a low-pressure compressor.
The high-pressure turbine and the low-pressure turbine may be controlled separately to adjust flow of exhaust gas. The exhaust gas flows through the high-pressure turbine and then through the low-pressure turbine when the engine is operating at low speeds. The flow of exhaust gas through the turbines can reduce response time of turbocharger boost, referred to as turbo lag.
The turbo lag may be controlled using a bypass valve (BPV) and a variable geometry turbine (VGT). The high-pressure turbine may include the BPV and the VGT. The VGT has a set of movable vanes that are used to control pressure of the exhaust gas flowing through the VGT. The flow of exhaust gas is low at low engine speeds. The vanes are partially closed to accelerate the VGT when the flow of exhaust gas through the VGT is low. Accelerating the VGT increases boost pressure delivered to the high-pressure compressor in the high-pressure turbocharger. As engine speed increases, the vanes are opened to reduce speed of the VGT. Reducing speed of the VGT prevents the boost pressure from exceeding a predetermined level. The BPV may open redirecting the flow of exhaust gas through the BPV when the VGT is operating at high speeds. The BPV relieves the boost pressure of the VGT before exceeding the predetermined level.